Projectile armor fabrication

ABSTRACT

A PROJECTILE ARMOR FABRICATION COMPRISING A COMPOSITE OF RELATIVELY RIGID, SMALL, SUBSTANTIALLY EQUAL SIZED LOAD DISTRIBUTING PLATELETS INTEGRATED WITHIN A MATRIX OF LESS RIGID MATERIAL; THE PLATELETS BEING ARRANGED WITHN THE MATRIX IN A SHINGLED, STATISTICAL, INTERPENDENT OR GEOMETRIC PATTERN, AND BEING BONDED THERETO WITH OR WITHOUT THE AID OF ADHESVES. THE COMPOSITE MAY BE FORMED AS A RELATIVELY LIGHT WEIGHT NON-RIGID SHEET AND EMPLOYED AS PERSONNEL ARMOR OR AS ARMOR PROTECTION FOR MILLITARY AIRCRAFT, VEHICLES, OR THE LIKE AGAINST SMALL ARMS FIRE. THE PLATELETS ARE DISTRIBUTED WITHIN THE MATRIX IN SUCH A MANNER AS TO PROVIDE IMPROVED DISTRIBUTION AND ABSORPTON OF PROJECTILE-IMPACT ENERGY AND TO DAMPEN THE ACCOUSTICAL ENERGY WAVE EFFECTS THEREOF BY CHANGING THEIR AMPLITUDES AND FREQUENCIES AS THEY ARE TRANSMITTED THROUGH THE COMPOSITE.

Feb. 16, 1971 J. D. DUNBAR PROJECTILE ARMOR FABRICATION 5 Sheets-Sheet 1 Filed May 23, 1968 INVENTOR.

JACK D. DUNBAR @a0/ 7 edf/,

ATTORNEYS Feb. 16, 1971 n J, D, DUNBAR 3,563,836

PROJECTILE ARMOR FABRICATION Filed May 23, 1968 5 Sheets-Sheet 2 INVENTOR.

JACK D. DUNBAR A TTORNEYS Feb. 16, 1971 J. D. DUNBAR PROJECTILE ARMOR FABRICATION 5 Sheets-Sheet 3 Filed May 23, 1968 INVENTOR` JACK D. DUNBAR @m @6m ATTORNEYS Feb. 16, 1971 I. D. DUNBAR PROJECTILE ARMOR FABRICATION 5 Sheets-Sheet 4 Filed May 25, 1968 Feb. 16, 1971 D DUNBAR 3,563,836

PROJECTILE ARMOR FABRICATION Filed May 23, 1968 5 Sheecs-SheerI 5 INVENTOR.

JACK D. DUN BAR United States Patent O 3,563,836 PROJECTILE ARMOR FABRICATION Jack D. Dunbar, Lewiston, N.Y., assignor to Bell Aerospace Corporation, Wheatfeld, N.Y. Filed May 23, 1968, Ser. No. 731,411 Int. Cl. B32b 3/14 U.S. Cl. 161-38 6 Claims ABSTRACT OF THE DISCLOSURE A projectile armor fabrication comprising a composite of relatively rigid, small, substantially equal sized load distributing platelets integrated within a matrix of less rigid material; the platelets being arranged withn the matrix in a shingled, statistical, interpendent or geometric pattern, and being bonded thereto with or without the aid of adhesves. The composite may be formed as a relatively light weight non-rigid sheet and employed as personnel armor or as armor protection for military aircraft, vehicles, or the like against small arms fire. The platelets are distributed within the matrix in such a manner as to provide improved distribution and absorpton of projectile-impact energy and to dampen the accoustical energy wave effects thereof by changing their amplitudes and frequencies as they are transmitted through the composite.

BACKGROUND OF THE INVENTION It has heretofore been proposed to form relatively flexible or non-rigid sheet like personnel armor comprising layers of rigid plates having laminated therebetween layers of elastic material. Specifically, in one prior armor construction disclosed in U.S. Pat. 2,723,214, plates forming each layer of plates are at and disposed in edge abutting relationship, and the area of individual plates forming each layer increases by a regular factor, such as 4, for each succeeding layer through the thickness of the armor.

This patent teaches that in order for the armor to work effectively, at least the relatively small plates forming the outermost layer of the armor must be suiciently rigid to prevent their being pierced or severely bent, so as to permit one of such plates when struck by a projectile, to move therewith in order to compress and thus transmit force through an adjacent layer of resilient material. It is asserted that as a result, kinetic energy of the projectile is converted into potential energy stored within the successively compressed layers of resilient material, which when forward movement of the projectile ceases, is reconverted into kinetic energy effective to accelerate the projectile in a reverse direction. Thus, it is suggested, the force transmitted to the wearer at the innermost surfact of the armor is the residue of force which has not been absorbed by compression of the resilient layers, and that such residual force is transmitted to the wearer over a very large area, compared to the area of the small plate originally struck by the projectile.

However, it can be demonstrated that as a practical matter, armor of the type discussed above cannot be employed as flexible light Weight armor, which is effective against hard nosed projectiles traveling at a high Velocity. In this respect, it is well known that presently available materials when formed into a small sized plate of the type proposed for use in the outermost layer of such armor are unable to withstand without complete failure due to melting or fracture, the impact of a hard nosed projectile traveling at high velocity. Accordingly, when armor of this type is struck with a hard nosed high velocity projectile, at least a plate in the first and probably several succeeding layers of plates will fail and be ice completely deformed before sufhcient kinetic energy is absorbed or converted to heat, accoustical and plate deforming energies in order to permit a plate in an intermediate layer of the armor to move along with the projectile without itself being deformed. This in effect requires that in order to reduce to a minimum the energy transferred through the armor to a wearer, the number of plate layers must be increased over that required if no plates were to fail. However, the number of plate layers which may be employed, is severely limited by the requirement that the armor be flexible. The problem as to flexibility will be appreciated when it is considered that when, as suggested in Pat. 2,723,214, the individual plate areas of successive layers increases as by a factor of 4, the probable practical limit is about 5 plate layers before the armor surface adjacent a wearer would become substantially rigid.

Further, it has been found that contrary to the patent teachings, normally resilient material, incorporated within a composite armor, when struck by a high velocity projectile, acts adjacent to the outwardly facng surface of the armor as a rigid body and thus does not elastically compress so as to readily absorb and convert kinetic energy of the projectile to potential energy.

SUMMARY OF THE INVENTION The present invention is directed towards a composite projectile armor fabricated by encapsulating a plurality of relatively rigid, small, substantially equal sized load distributing platelets wthin a matrix formed of a relatvely less rigid materal; the platelets being arranged within the matrix in a shingled, statistical, interdependent or geometric pattern chosen to position a desired number of platelets in alignment with any possible path of movement of a projectile through the armor. The configuration and dimensions of the platelets are related to the thickness of the encapsulating matrix material so as to provide an improved distribution of projectible impact shock stresses within the composite and thus minimize the overall thickness and weight thereof.

IContrary to prior armor composites, the armor of the present invention is adapted to absorb the primary impact energy of a projectile, as expressed in pressure and acoustical wave stresses, through visco-elastic-plastic shear loadings on the relatively large cumulative plateletmatrix inner face areas or surfaces, in addition to conventional energy absorption factors including material inertia, elastic and plastic strain and failure initiation propagation.

More specifically, in accordance with the preferred embodiment of the present invention, the composite armor is in the form of a relatively light weight non-rigid or relatively flexible sheet defined by a matrix of elastomeric material in which is embedded small, substantially equal sized, discoid shaped metallic platelets arranged in layers. Preferably, the platelets have a double conical configuration, wherein the ratio of platelet diameter to thickness is greater than about 10, and are rmly bonded about substantially the entire surface thereof to the matrix, so as to maximize the transfer of elastic-plastic shear forces therebetween.

The composite may be formed by overlying layers of uncured elastomeric material and platelets and thereafter subjecting the composite to heat and pressure in order to cure or set the elastomer and form the composite into a desired shape. The platelets may be individually formed and laid separately to form each platelet layer. Alternatively, the platelets defining each platelet layer may be formed by roller or stamp embossing a plain sheet of metallic material in such a manner that the platelets will remain attached to one another in sheet form with a thin `foil interconnecting tie. The tie is preferably broken by roller deforming or fiexing the composite prior to curing or setting of the matrix. However, if the thickness of the tie is sufficiently small with respect to the dimensions of the platelets, the tie may be left intact within the composite without severely effecting the performance thereof.

The nature and manner of operation of the armor of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings herein:

FIG. l is a fragmentary schematic view of the armor of the present invention illustrating the general distribution of stresses throughout the armor due to the impact of a projectile;

FIG. 2 is a fragmentary plan view of the outermost layer of platelets of the armor of the present invention;

FIG. 3 is a view similar to FIG. 2, but illustrating the placement of platelets in a first adjacent intermediate layer of the armor;

FIG. 4 is a view similar to FIG. 3, but illustrating the placement of platelets of a second intermediate layer of the armor;

FIG. 5 is a perspective view on a substantially enlarged scale showing the preferred platelet configuration employed in the practice of the present invention;

FIGS. 6 and 7 are perspective views on a substantially enlarged scale of possible alternative discoid platelet configurations adapted for use in the present invention; and

FIG. 8 is a view illustrating a platelet fabrication permitting economical forming and positioning of a platelet layer within the armor composite matrix.

To facilitate understanding of the present invention, composite armor formed in accordance therewith is designated generally as 1 and illustrated schematically in FIG. 1 as being sheet like in for-m and as having a plurality of relatively rigid platelets 10 which are ernbedded within a relatively less rigid matrix and disposed within a desired number of layers, as for instance those generally designated as layers A-G. As will be more fully hereinafter discussed, the number of platelet layers provided in any given composite will depend upon the type of projectile to be arrested, the platelet configuration and spacing and the composition of the platelets and matrix employed.

In accordance with the preferred embodiment of the present invention, the armor composite is of a non-rigid construction, wherein the matrix is formed from a suitable elastomeric material, such as natural rubber, and the platelets are in the form of small, substantially equal sized discoids of steel having a double conical configuration, as depicted in FIG. 5. Discoid shaped platelets have been found to be most effective when formed with a diameter which is greater than about l0 times the thicky ness thereof. The platelets may, however, effectively range in size from several microns to several inches in diameter depending on the caliber and velocity of projectile to be arrested by the composite.

The utilization of substantially equal sized discoids, when arranged within the composite in the manner to be hereinafter described, permits the composite to exhibit a remarkable degree of flexibility.

The composite may be fabricated by laying individual platelets in layers between sheets of matrix forming material until a desired number of platelet-matrix layers are obtained, and thereafter subjecting the composite to heat and pressure in order to cure or set the matrix forming material and form the composite into a desired shape. The composite when formed within a mold having fiexible walls, has, as indicated in FIG. l, uneven outer and inner side surfaces, and 26 respectively, which may be characterized as being pebbled in appearance. Clearly, however, the side surfaces 25, 26 may be fiat if desired.

CII

FIGS. 2, 3, and 4 are fragmentary plan views illustrating the relative placement of discoid shaped platelets in the first three platelet layers A, B and C, respectively; the platelets of layer A being shown in full line with vertical edge shading; the platelets of layer B being shown in medium dashed line with horizontal edge shading; and the platelets in layer C being shown in light weight dashed line with inclined edge shading.

Referring specifically to FIG. 4 it will be seen that the platelets within each of layers A-C are arranged in a uniform geometric pattern and that the patterns of the respective layers are relatively offset or staggered, so as to present a three layer, composite solid metal obstacle to the passage of a projectile striking surface 25 of the composite. "It will be understood that succeeding layers of platelets sequentially repeat the platelet patterns of layers A, B and C, such that the platelets of for instance layers A, D and G are disposed in alignment. Although other platelet patterns are susceptible of use depending on the configuration of platelets employed, the pattern arrangement illustrated in FIG. 4 has been found preferable for discoid shaped platelets where relative flexibility of the composite in all directions is desired, without the need to resort to incerased edge spacing between platelets of respective layers.

Preferably, in the case where the platelets having a double conical configuration of the type shown in FIG. 5 are positioned within the composite, oppositely facing apex portions of the platelets with any given layer, as for instance layer B, project into adjacently disposed platelet layers, as for instance layers A and C, as indicated schematically in FIG. l. This arrangement insures that no platelet free or unobstructed path exists through the composite regardless of the angle at which a projectile strikes the composite. The preferred thickness of the matrix between conically shaped surfaces of platelets of adjacent layers has been determined to be on the order of about l5 of the thickness of an individual platelet. It is believed that this arrangement maximizes the impact energy dissipating capabilities of the matrix. The area of preferred thickness referred to above is shown in FIG. 3 as being for instance between platelet 10a of layer A and closely adjacent platelets 10b of layer B and as lying along heavy broken lines 28.

It will pe understood that the double conically shaped platelets of the type shown in FIG. 5 have what may be characterized as an effective target area which is only about 1/2 their diameter, due to the fact that the remaining peripheral edge portions thereof are too thin to effectively retard projectiles until a sufficient portion of the impact energy is dissipated within the composite. While at first such relatively small effective target area, when compared to afiat disc of equal diameter and overall thickness, would seem undesirable due to the fact that additional platelet layers would be required, it has been found that weight savings per platelet, which permits the utilization of additional platelet layers (assuming the weight of additional matrix layers are negligible by comparison) serves to increase effectiveness of the composite without an increase in the weight thereof. Alternatively, the same degree effectiveness may be obtained at a reduction in composite Weight. This phenomena will be more readily understood by considering that for any given total platelet weight, double conically shaped platelets, as compared with flat discoid platelets, have both relatively larger platelet-matrix innersurface areas which are operable to dissipate impact energies by shear loading, and relatively larger sectional or plan areas which are operable to rassist in `dissipating impact energy by elastic compression of adjacent matrix layers.

Further, it has been determined that double conically shaped platelets are more effective than fiat discoids of the same dia-meter and thickness for the purpose of deliecting projectiles during passage thereof through the composite at the same angle of inclination.

For purposts of reference and in order to simplify the present discussion, it will be assumed that a projectile 31 upon striking the outwardly facing surface 25 of the composite, as indicated at FIG. 1, is traveling along a path disposed normal to the general plan defined by the composite and initially strikes centrally the platelet a, shown in each of FIGS. 1, 2, 3 and 4.

To further simplify the discussion, it will be assumed that, contrary to actual practice, platelet 10a upon impact is moved toward composite surface 26 Without failure or deformation thereof, thereby setting up a cone of compression stress, indicated generally in FIG. 1, within which compressive force is transferred from platelet 10a to platelets 10b, to platelets 10c, through the intervening platelet matrix layers, as indicated in FIG. 4. The effect is threefold, namely, greater and greater amounts of impact energy are converted and stored as potential energy within the elastically and plastically deformed matrix layers disposed within the cone of compression; impact energy is dissipated by innersurface shear loading between platelets in successive layers and the intervening matrix layers within the cone of energy absorption due to shear loading also generally indicated in FIG. l; and the remaining or non-dissipated impact energy, which is transferred to a wearer at surface 26, is distributed over an area substantially greater than the area of impact, so as to proportionately reduce the intensity thereof. If on the other hand it were to be assumed that upon impact, a projectile strikes the effective target area of for example, one of platelets 10c, rather than 10a, then initiation of impact energy dissipation in the manner described 'would be slightly delayed.

As indicated in FIG. l, the cone of energy absorption due to shear has a greater cone angle than the cone of compression, due to the fact that shear forces are set up along conically shaped platelet surfaces arranged substantially transversely of the path of projectile 31, whereas compression stress is distributed substantially normal to the composite. The arrows, designated in FIG. l as 50, represent equal and opposite shear force reactions on platelet matrix inner surfaces for adjacent platelets. It will be understood that the lengths of arrows 50 indicated the amount of impact energy dissipated due to inner surface shear considerations at any given point; the magnitude of the impact force dissipated progressively decreasing as the relative movement of the respective platelets produced by impact energy decreases.

Arrows 50 additionally serve to indicate the general distribution and mode of damping acoustical waves set up by impact of a projectile. In this respect it will be understood that acoustical energy is dissipated in passing any given platelet-matrix interface due to incomplete conversion of energy between bodies having differing natural frequencies of vibration. Thus, it will be apparent that as the wave progresses through the the composite, the energy thereof will be progressively diminished per unit area of the matrix, as indicated by the progressive shortening of arrows 50i, since more and more platelets and matrix in successive layers are effected. It is believed that double conically shaped platelets are more effective than other discoid configurations, since their conically shaped surfaces function to distribute the wave in directions other than normal to the plane of the composite.

It has been found by actual firing tests that platelets in the first layer or layers of platelets melt or vaporize adjacent to the point of impact, and platelets in the next several layers fail by fracture, before the impact energy of a projectile is reduced by heat and platelet failure considerations to a degree which permits a platelet, which is sequentially encountered by the projectile to move while in one piece, toward composite surface 26. Further, examination of test specimens, indicates that there is substantial elastic and plastic bending of platelets within the cone of compression which aids in dissipating impact energy. As a result, the shapes of the actual shear load- 6 ing and compression distributions may vary from the ideal distributions shown in FIG. 1.

FIGS. 6 and 7 illustrate alternative discoid platelet configurations 10 and 10, respectively, which may be successfully substituted for the preferred platelet configuration shown in FIG. 5 in the practice of the present invention, although with diminishing degrees of effectiveness.

In FIG. 6 opposing surfaces of the platelet 10 are shown as being rounded. When employing this configuration, the overall weight of the platelet and the overall thickness of the composite is increased slightly over that obtainable by employing the double conically shaped platelet discussed above. Additionally this configuration forms with the matrix an interface surface which is less effective with respectrto shear loadings than a double Y conical platelet. However, this configuration does lend itself to the economical fabrication of extremely small sized metallic platelets or those formed from ceramics and impregnated fabrics.

In FIG. 7, the platelet 10 is shown as being in the form of a fiat disc. This platelet configuration is least effective of the platelet configurations described for use in a composite armor from the standpoint of shear loading and composite weight and thickness considerations. However, it may be more economically fabricated. and does offer a greater effective target area per platelet for a given platelet edge spacing, i.e. evenly distributed mass, whereby a given layer of such platelets offers a greater likelihood of its being effective in slowing the speed of a projectile. The latter desirable features of the flat disc platelet may be taken advantage of by forming a composite, wherein upwards of the first three outwardly facing platelet layers of the Composite are defined by at discs and the remaining platelet layers are defined by discoids of the type shown in either of FIG. 5 or 6. In such a composite, the outer platelet layer or layers, which will likely be subjected to complete failure due to the impact energy of the projectile, serve to insure effective kinetic energy dissipating contact of a projectile with a platelet upon initial penetration of the composite, whereas the remaining platelet layers which are not subject to complete failure serve to effectively dissipate the remaining impact energy through platelet-matrix intersurface shear.

FIG. 8 illustrates an alternate platelet fabrication which may be formed by roller or stamp embossing a plane surfaced sheet of metal to define a plurality of discoid shaped platelets interconnected by a thin frangible foil tie 11. The preferred thickness of tie web 11 has been determined to be on the order of about lm the thickness of the platelets. This fabrication not only permits the platelets to be formed relatively inexpensively. but permits all of the platelets of a layer to be laid simultaneously and thus greatly reduces assembly costs. Preferably, tie 11 is broken by roller deforming or flexing the cornposite prior to the curing or setting of the matrix in order to permit direct bonding of adjoining matrix layers and insure complete encapsulation of the individual platelets. Particularly where the tie is sufficiently thin with respect to the dimensions of the platelets and/or where portions of the tie are removed or punched out prior to forming the composite in order to permit bonding between portions of adjoining matrix layers, the ties may be left intact within the composite without severely affecting the performance thereof.

Further, in referring to FIG. 8, it will be understood that the edges of the platelets employed in the practice of the present invention may be spaced apart a distance up to less than about 1/2 the diameter thereof, without destroying the effectiveness of the composite.

For the purpose of demonstrating the practicability of the concepts discussed above, composite specimens and conventional solid armor plate samples were prepared and comparative tests conducted.

The composite specimens were each formed by laminating under heat and pressure 30 layers of double conically shaped platelets formed from 8620 steel carbonized nominally to 60 RC, and 31 layers or sheets of natural rubber, each sheet having an initial thickness of 0.020 inch. The platelets within each layer had a 0.006 inch nominal edge spacing and the platelet layers were staggered in the manner indicated generally in FIG. 4. Each platelet had a diameter of 0.6 inch, a maximum thickness of 0.04 inch and a weight of 9 grains. After fabrication, each composite specimen had an overall thickness of 0.97 inch, a total platelet weight of 13.2 pounds per square foot of composite surface area, a total composite weight of 17 pounds per square foot of composite surface area, and a platelet-matrix inner surface shear bond strength determined to be about 300 pounds per square inch. The composite specimens were sufficiently exible to permit bending.

Reference solid armor plate samples were prepared from 8620 steel carbonized nominally to 60y RC with a thickness of approximately 0.33 inch to produce plate samples having a weight per plate surface area identical to the platelet weight of the composite specimens.

Comparative firing tests were conducted on five composite specimens and ve solid armor plate samples with 22 caliber long rifle ball, 30 caliber special ball, 45 caliber ball, 30 caliber M-l ball and 30 caliber M-2 armor piercing ammunition, using a test firing stand, including in face to face stacked relationship a paper target sheet, the test specimen or sample, a block of high density polystyrene foam, a 0.03 inch aluminum witness puncture plate and a block of paper back-up sheets. The paper target sheet, the foam block and aluminum witness sheet offered substantially no resistance to projectile penetration. For further reference, firing tests were conducted with 30 caliber M-l ball and 30 caliber M-2 armor piercing ammunition fired only through a target sheet, an aluminum witness puncture plate and paper back up sheets. All projectiles were fired from 30 yards, except for the 45 caliber ball, which was fired at 15 yards for purposes of accuracy, and all projectiles had an impact angle of 90.

The results obtained from the firing tests are tabulated below.

eters of the composite, either individually or collectively, including individual platelet weight, or platelet geometry in the outwardly facing layer or layers of the composite, or the platelet-matrix inner surface shear bonding strength.

Examination of the composite specimen impacted by a 45 caliber ball clearly demonstrated the effectiveness of the utilization of matrix-discoid-platelet innersurface shear forces to dissipate projectible energy.

While platelets 1,0 have been described as being formed from steel, they may, however, be formed from other metals or metal alloys including aluminum and titanium. Alternatively, the platelets 10 may be formed from intermetallics, ceramics, carbides, organic material, such as a polycarbonate, and laminates of various fabrics which are impregnated or filled with thermoplastic or thermosetting resinous materials. In addition to the utilization of natural rubber as the matrix forming material, various other elastic, Visco-elastic or flexible plastic materials may be effectively employed. 4Exemplatory thereof would be GR-S; GRAN; chlorinated rubber, neoprene; polyisobutylene; urethanes; polyesters; polysulfones; nylons; silicones; polyfluorinated hydrocarbons; acrylates such as substituted and unsubstituted polyethyl and methyl methacrylates and polyethyl and methyl acrylates; cellulose resins, such as alkyl cellulose, cellulose acetate, cellulose butyrate, and mixed cellulose esters; vinyl resins, such as polyvinyl chloride, polyvinylidine chloride, and copolymers thereof, such as polyvinyl acetals, particularly polyvinyl butyral, which may be modified by cross-linking agents and styrenes, such as substituted and unsubstituted polystyrene. Further, present available ablative materials, including rubber, may be employed in forming matrix in order to further increase the effectiveness of the composite with respect to armor piercing projectile.

While the present invention has been described with particular reference to its use as a non-rigid armor sheet, it will be understood that the sheet may be of rigid construction, wherein the matrix is formed from non-elastomeric materials including metals, providing that the rigidity of the matrix is relatively less than that of the individual platelets. Further, the composite may be fabricated in other than flat sheet form, as for instance as a cylinder Platelet-rubber composite Reference platel inch .Paper Front backing face Rear Front Rear only, Weight Muzzle Energy peneface Paper face face Paper paper .in velocity in tration, tear pene- Front penepenepene- Front pene- Amo grains ft. /sec. ft./lbs. platelets out tration splatter tration tration tration splatter tration 22 caliber L.R. ball. 40 l, 335 158 10 0 0 0 Dimple... 0 0 Negative No test. 30 caliber special ball. 158 855 256 l2 0 0 0 Diniple O 0 Significant.. D0. 45 caliber ball 210 775 247 l2 0 0 0 Dimple. 0 0 do Do. 30 caliber M-l ball 150 2, 970 2, 930 5 1 2 Si 1% 0 Dimple- 0 30 caliber M-2 Al 165 2, 700 2, 900 51 2 3 2% 0 3 (3) 2 Plates collected IPunch cylindrical hole.

From the above tabulation, it will be seen that both composite specimens and solid armor plate samples were effective in arresting 22 caliber long rifle ball, 30 caliber special ball and 45 caliber ball ammunition, and that the composite specimen effectively prevented projectile splattering on the impact surface for all test firings. lt will also be seen that the composite specimens were effective in absorbing upwards of two-thirds of the available impact energies of the 30 caliber M-l ball and 30 caliber M-Z A.P. ammunition, whereas the reference solid armor plate sample was effective in absorbing only about one-third of the available impact energy of the 30 caliber M-2 A.P. ammunition.

Present theory is unable to explain the anomaly which apparently exists in the case of the composite test specimen impacted with a 30 caliber M-l ball. While further tests will be conducted to determine the accuracy of this test, it is believed that even if valid, penetration by a 30 caliber M-l ball in addition to the 30 caliber M-2 A.P. may be completely arrested by changing certain paramfor the purpose of protecting aircraft control cables or as a curved sheet conforming to the contour of any object to be protected.

Still further, platetlet surfaces may if desired be roughened or serrated in order to complement or take the place of an adhesive or other bond between the platelets and matrix for the purpose of providing that degree of interlocking necessary to insure a desired shear force interface loading distribution. Additionaly, it is anticipated that platelets of other than a discoid configuration may be employed in the practice of the present invention. For instance, flat and single or double pyramid shaped platelets of rectangular or square section would be desirable, particularly when employed in one or more of the outwardly facing layers of the composite for the purpose of presenting a greater effective target area per layer. Furthermore, for specific applications, the characteristics of the composite including its degree of exibility can be tailored by changing certain parameters individually or collectively,

eg. platelet material, geometry or distribution, or matrix material.

I claim:

1. A projectile armor fabrication comprising a composite of relatively rigid, small, substantially equal sized toad distributing platelets encapsulated with a matrix formed of a relatively less rigid material, said platelets being arranged in spaced layers within the composite, the platelets within a least three adjacent layers being arranged in a given platelet pattern, the patterns of said adjacent layers being relatively staggered so as to present a three layer composite solid platelet obstacle to the passage of a projectile therethrough, and said platelets in at least said adjacent layers being of double-conical conguration having a ratio of diameter to thickness equal to or greater than about 10.

2. A projectile armor fabrication according to claim 1, wherein oppositely facing apex portions of platelets within an intermediate platelet layer project into spaces between platelets of immediately adjacent layers of platelets.

3. A projectile armor fabrication according to claim 2, wherein said platelets are metallic, said matrix forming material is an elastomer, and the spacing between platelets of adjacent layers is on the order of about 1/15 the thickness of an individual platelet.

4. A projectile armor fabrication comprising a composite of relatively rigid, small, substantially equal sized load distributing platelets encapsulated with a matrix formed of relatively less rigid material, said platelets being arranged in spaced layers within the composite, said platelets within said layers being edge joined by a frangible integrally formed tie portion, the platelets within at least three adjacent layers being arranged in a given platelet pattern, and the patterns of said adjacent layers being relatively staggered so as to present a three layer composite solid platelet obstacle to the passage of a projectile therethrough.

S. A projectile armor fabrication according to claim 4 wherein said platelets are discoids having a ratio of diameter to thickness equal to or greater than about 10, and the thickness of said tie portion is on the order of about 1/150 the thickness 0f said discoids.

6. A projectile armor fabrication according to claim 5, wherein said discoids have a double-conical conguration, and oppositely facing apex portions of platelets within an intermediate platelet layer project into spaces between platelets of immediately adjacent layers of platelets.

References Cited UNITED STATES PATENTS 3,431,818 3/1969 King 161--404UX 2,723,214 11/1955 Meyer 161-38 2,768,919 10/1956 Bjorksten et al. 161-37 PHILIP DIER, Primary Examiner U.S. Cl. XR. 

